The present invention relates, as indicated, to a thermistor airflow sensor assembly and relates more particularly to a sensor assembly for monitoring the breathing of patients.
Sleep apnea is a term used to refer to a temporary break or suspension in respiration, and frequently occurs in persons of all ages. It is a particularly difficult problem with infants. There are various methods of monitoring sleep apnea, with one of these comprising the monitoring of the breathing cycle. The use of thermistors is widely known for this purpose, with the thermistor sensing quickly and accurately the differences between ambient temperature and the temperature of the expired air, and changing its resistance in response thereto. This change in resistance can be visually displayed.
In thermistor sensor systems, a thermistor is typically placed adjacent each nostril or naris of the nose and also adjacent the mouth so that nasal and oral airflow, respectively, can be monitored. When the patient or user is breathing normally, the monitoring device to which the thermistors are connected will provide a read out indicative of normal breathing. The absence of temperature change is indicative of at least a temporary cessation of expiration of air, and this condition can be quickly read out visually on the monitor as well as actuating an audible alarm. As described, merely the presence or absence of breathing is detected by the monitoring system, although more sophisticated systems can be utilized which additionally monitor the temperature and quantity of air expired, moisture content, etc.
The use of thermistors for the purpose indicated has in the past presented certain problems with respect to the mounting of the thermistors on the user. Typical arrangements still in use at this time comprise the use of thermistor beads attached to wires which must be taped to the face of the user and arranged under the nose and in front of the mouth of the user. This arrangement has obvious disadvantages. The taping is inconvenient, unsightly, and frequently ineffective since the tape can be pulled from the face and the monitoring function thus disrupted. Moreover, a taped mounting of this type is very uncomfortable and lacks durability since the thermistor beads and connecting wires are freely exposed for possible damage.
A proposed solution to the above problem is disclosed in U.S. Pat. No. 4,777,963, in which thermistors adapted to be placed adjacent the naris and mouth are carried by a support member which includes a removable release paper which when stripped away uncovers an adhesive surface for securing the support member to the skin of the patient. The support member includes an upper portion which can be bent to contact the user over the bridge of the nose and the areas on each side thereof. A second, lower portion, carries the thermistors and can be folded upwardly so that such portion is adhesively attached to the face of the wearer below and to either side of the nose, and between the nose and the lips. The oral thermistor extends downwardly from the lower portion so that it can be positioned outwardly of the mouth for receiving orally expired air.
Although the respiration monitor disclosed in U.S. Pat. No. 4,777,963 does solve certain of the earlier problems noted, it too has clear disadvantages. The construction is such that manual assembly of the thermistors and lead wires therefor on the support member is necessary. All thermistors are exposed which, because of their relatively small size and brittle nature, can lead to premature damage. The possibility of thermistor damage is recognized by patentee who provides both a mesh covering and an outer elastic sleeve around the thermistors to guard against potential inhalation of fragments of the thermistors in the event the thermistors are broken. This precautionary measure is time consuming and adds to the cost of the assembly. Further, the ability of the device to firmly seat on the patient varies tremendously with the facial configuration of the patient. This increases the potential for misalignment of the thermistors with the nostrils.